1. Field of the Invention
The present invention relates to interactive broadband server systems, and more particularly, to virtual file system that manages and maintains information of data distributed across an array of storage devices.
2. Description of the Related Art
It is desired to provide a solution for the storage and delivery of streaming media content. An initial goal for scalability is from 100 to 1,000,000 simultaneous individual isochronous content streams at 4 megabits per second (Mbps) per stream, although different data rates are contemplated. The total bandwidth available is limited by the largest available backplane switch. The largest switches at the present time are in the terabit per second range, or about 200,000 simultaneous output streams. The number of output streams is generally inversely proportional to the bit rate per stream.
The simplest model of content storage is a single disk drive connected to a single processor which has a single network connector. Data is read from the disk, placed in memory, and distributed in packets, via a network, to each user. Traditional data, such as Web pages or the like, can be delivered asynchronously. In other words, there are random amounts of data with random time delays. Low volume, low resolution video can be delivered from a Web server. Real time media content, such as video and audio, require isochronous transmission, or transmission with guaranteed delivery times. In this scenario, a bandwidth constraint exists at the disk drive. The disk has arm motion and rotational latency to contend with. If the system can only sustain 6 simultaneous streams of continuous content from the drive to the processor at any given time, then the 7th user's request must wait for one of the prior 6 users to give up a content stream. The upside of this design is simplicity. The downside is the disk, which, as the sole mechanical device in the design, can only access and transfer data so fast.
An improvement can be made by adding another drive, or drives, and interleaving the drive accesses. Also, duplicate content can be stored on each drive to gain redundancy and performance. This is better, but there are still several problems. Only so much content can be placed on the local drive or drives. The disk drives, CPU, and memory are each single points of failure that could be catastrophic. This system can only be scaled to the number of drives the disk controller can handle. Even with many units, there is a problem with the distribution of titles. In the real world, everyone wants to see the latest movies. As a rule of thumb 80% of content requests are for just 20% of the titles. All of a machine's bandwidth cannot be consumed by one title, as it would block access to less popular titles stored only on that machine. As a result, the “high demand” titles would have to be loaded on most or all of the machines. In short, if a user wanted to see an old movie, that user might be out of luck—even though it is loaded in the system. With a large library, the ratio may be much greater than the 80/20 rule used in this example.
If the system were based on the standard Local Area Network (LAN) used in data processing, there would be other inefficiencies. Modern Ethernet-based TCP/IP systems are a marvel of guaranteed delivery, but include a time price caused by packet collisions and re-transmits of partially lost packets and the management needed to make it all work. There is no guarantee that a timely set of content streams will be available. Also, each user consumes a switch port and each content server consumes a switch port. Thus, the switch port count has to be twice the server count, limiting the total online bandwidth.